The present invention relates generally to the field of welding systems, and more particularly to power sources used for creating high frequency, high voltage, low current pulses used to initiate and maintain arcs in such systems for the purpose of welding or cutting.
A wide range of welding techniques have been proposed and are presently in use. In general, welding of metals is performed by melting one or more base metals in a work piece, as well as an adder metal in certain applications. One particularly useful welding technique, well suited for precise or intricate welding, is tungsten inert gas (TIG) welding. In TIG systems, a metal electrode, typically made of tungsten, is provided in a welding torch, and is generally not consumed (i.e., added to the base metal) during welding. Electric current is channeled through the electrode, and a flow of a shielding gas surrounds the electrode during the welding operation, generally provided by fluid conduits leading to the welding torch. An arc is struck between the electrode and the workpiece to melt the workpiece. Adder metal can be provided but, in general, welding takes place by the fusion of the workpiece metals.
As opposed to certain other welding techniques, in TIG welding applications, it is desirable to strike and maintain an arc with little or no contact between the electrode and the workpiece. However, the arc itself may be somewhat difficult to strike and maintain based upon the welding power alone. Therefore, to aid in striking and maintaining the arc, a welding power supply may be designed to superimpose a high frequency, high voltage, low current waveform on a base waveform applied to the welding electrode via the welding torch. When welding with DC power, the high frequency pulse train may be provided only during start-up or loss of the arc. In AC welding, the pulse train may similarly be provided during start-up, but may also be provided continuously, where desired, so as to stabilize the arc and prevent the arc from being rectified or extinguished during polarity reversals of the AC waveform (zero cross). The systems may sense whether an arc is established or maintained in order to provide closed loop control of the application of the high frequency waveform accordingly.
High frequency waveforms for establishing and maintaining arcs in TIG welding systems have typically been provided by a high frequency arc starter circuit. Such circuits may utilize electronic or capacitive discharge methods to deliver high frequency energy directly or through a coupled inductor to the welding torch to initiate non-contact arc starting. For example, a capacitor may be charged to a relatively constant voltage. Once the voltage level is reached, the capacitor is discharged, releasing the stored energy to the welding torch to ionize a gas column to initiate an arc start or re-ignition (AC arcs).
Although using a relatively constant voltage for initiating and maintaining arcs in TIG welding systems functions adequately, it is not without drawbacks. In certain welding applications, it may be desirable to increase or decrease the amount of high frequency energy in the arc. For example, when welding at low currents (i.e. below 10 amps), it is desirable to have less high frequency energy in the arc to re-ignite at zero cross. Too much high frequency energy may cause excessive heat build up and result in a poor quality weld. Furthermore, reducing the amount of high frequency energy may also reduce the amount of electro-magnetic interference (EMI).
For other welding applications, it may be desirable at times to increase the amount of high frequency energy in order to overcome leakage paths in the welding torch or in other components of the welding system.
To avoid the drawbacks of the prior art, there is a need, therefore, for an improved welding power supply with a variable high frequency output for optimizing the delivery of high frequency energy for different welding applications.